As a device which detects values of electrostatic capacitances which are distributed in a matrix manner, PTL 1 discloses a touch panel device which detects (estimates) distribution of values of respective electrostatic capacitances of an electrostatic capacitance matrix formed between K drive lines and L sense lines.
The touch panel device described in PTL 1 above, when a user touches a touch panel with an object to be detected such as a finger or a pen, detects a change (for example, decrease) in a value of an electrostatic capacitance at a touched position to thereby detect the position on the touch panel, which is touched by the user.
Specifically, a touch panel system 100 described in PTL 1 includes a touch panel 101 and a touch panel controller 110 as illustrated in FIG. 9. The touch panel 101 includes four drive lines DL1 to DL4 (K=4) and four sense lines SL1 to SL4 (L=4), and electrostatic capacitances C11 to C44 are respectively formed at positions where the drive lines DL1 to DL4 and the sense lines SL1 to SL4 intersect with each other.
The touch panel controller 110 is provided with a driving unit 111, and the driving unit 111 drives the drive lines DL1 to DL4 based on code sequences. As the code sequences, specifically, an M-sequence which is a binary pseudo random number sequence with a sequence length of N=31 is used as indicated in FIG. 10.
Here, description will be given by assuming that Drives 1 to 4 in the code sequences with the sequence length of N=31 indicated in FIG. 10 are allocated as signals for driving the drive lines DL1 to DL4. Elements of the code sequences are either “1” or “−1”.
The driving unit 111 applies a voltage “Vdrive” illustrated in FIG. 9 when the element of the code sequence is “1”, and applies “−Vdrive” when the element of the code sequence is “−1”.
The touch panel system 100 has two differential amplifiers 112 which are connected to the sense lines SL1 and SL2 and the sense lines SL3 and SL4. The differential amplifiers 112 receive linear sum signals based on respective electrostatic capacitances C11 to C14, C21 to C24, C31 to C34 and C41 to C44, which are output from the sense lines SL1 to SL4 when the driving unit 111 drives the drive lines DL1 to DL4, and amplify a difference thereof.
Here, an operation of the touch panel system 100 will be described by exemplifying an operation of the differential amplifier 112 to which the sense lines SL3 and SL4 are connected.
The driving unit 111 drives the drive lines by the four Drives 1 to 4 among Drives 1 to 31 indicated in FIG. 10.
For example, the driving unit 111 applies the voltage “Vdrive” to the drive lines DL1, DL3 and DL4 and applies the voltage “−Vdrive” to the drive line DL2 in driving with a 1st Vector indicated in FIG. 10. At this time, an input and an output of the differential amplifier 112 are short-circuited, an integration capacitance Cint which is connected to the differential amplifier 112 is in a reset state, and all the sense lines are operated to have a voltage of zero. That is, in a case where charges accumulated in the electrostatic capacitances C31 to C34 and C41 to C44 are Q31 to Q34 and Q41 to Q44, respectively, when a charge amount is calculated with a sense line voltage as a reference, Q31 to Q34 and Q41 to Q44 are provided byQ31=−Vdrive·C31, Q32=−Vdrive·C32, Q33=−Vdrive·C33, Q34=−Vdrive·C34 Q41=−Vdrive·C41, Q42=−Vdrive·C42, Q43=−Vdrive·C43, Q44=−Vdrive·C44.  [Expression 1]
Note that, electrostatic capacitance values of the electrostatic capacitances C11 to C44 are indicated by C11 to C44, respectively.
Next, a state where a short-circuit state of the differential amplifier 112 is released is considered. The driving unit 111 operates all the drive lines to have a voltage of zero. When respective input voltages of the differential amplifier 112 are X3 and X4 and respective output voltages are Y3 and Y4, sums QY3 and QY4 of charges accumulated in capacitances connected to the differential amplifier 112 are provided byQY3=X3·(C30+C32+C33+C34)+(X3−Y3)Cint QY4=X4·(C41+C42+C43+C44)+(X4−Y4)Cint.  [Expression 2]
In accordance with the law of conservation of charge,QY3=Q31+Q32+Q33+Q34 QY4=Q41+Q42+Q43+Q44  [Expression 3]
are established, and the output voltages Y3 and Y4 of the differential amplifier 112 are respectively provided by
                                 {                                                                                                                                                                                                                                                            X                                ⁢                                                                                                                                  ⁢                                                                  3                                  ·                                                                      (                                                                                                                  C                                        31                                                                            +                                                                              C                                        32                                                                            +                                                                              C                                        33                                                                            +                                                                              C                                        34                                                                                                              )                                                                                                                              +                                                                                                (                                                                                                            X                                      ⁢                                                                                                                                                          ⁢                                      3                                                                        -                                                                          Y                                      ⁢                                                                                                                                                          ⁢                                      3                                                                                                        )                                                                ⁢                                                                  C                                  int                                                                                                                      =                                                                                                                                                                                                                                          -                                                                  V                                  drive                                                                                            ·                                                              C                                31                                                                                      +                                                                                          V                                drive                                                            ·                                                              C                                32                                                                                      -                                                                                          V                                drive                                                            ·                                                              C                                33                                                                                      -                                                                                          V                                drive                                                            ·                                                              C                                34                                                                                                                                                                                                                                                                                                                                                                                                                X                                ⁢                                                                                                                                  ⁢                                                                  4                                  ·                                                                      (                                                                                                                  C                                        41                                                                            +                                                                              C                                        42                                                                            +                                                                              C                                        43                                                                            +                                                                              C                                        44                                                                                                              )                                                                                                                              +                                                                                                (                                                                                                            X                                      ⁢                                                                                                                                                          ⁢                                      4                                                                        -                                                                          Y                                      ⁢                                                                                                                                                          ⁢                                      4                                                                                                        )                                                                ⁢                                                                  C                                  int                                                                                                                      =                                                                                                                                                                                                                                          -                                                                  V                                  drive                                                                                            ·                                                              C                                41                                                                                      +                                                                                          V                                drive                                                            ·                                                              C                                42                                                                                      -                                                                                          V                                drive                                                            ·                                                              C                                43                                                                                      -                                                                                          V                                drive                                                            ·                                                              C                                44                                                                                                                                                                                                                    ⁢                                                          ⁢              and              ⁢                                                          ⁢              thus                        ,                                                  ⁢                          {                                                                                                                                            Y                          ⁢                                                                                                          ⁢                          3                                                =                                                                                                                                                                                                                                                                                                                                                                                                                                    V                                              drive                                                                                        ·                                                                                          C                                              31                                                                                                                                -                                                                                                                                    V                                              drive                                                                                        ·                                                                                          C                                              32                                                                                                                                +                                                                                                                                    V                                              drive                                                                                        ·                                                                                                                                                                                                                                                                                                                                                                    C                                            33                                                                                    +                                                                                                                                    V                                              drive                                                                                        ·                                                                                          C                                              34                                                                                                                                                                                                                                                                                                                C                                    int                                                                                                  +                                                                                                                                                                                                                                          X                                  ⁢                                                                                                                                          ⁢                                                                      3                                    ·                                                                          (                                                                                                                        C                                          31                                                                                +                                                                                  C                                          32                                                                                +                                                                                  C                                          33                                                                                +                                                                                  C                                          34                                                                                +                                                                                  C                                          int                                                                                                                    )                                                                                                                                                                        C                                  int                                                                                                                                                                                                                                                                                                                      Y                          ⁢                                                                                                          ⁢                          4                                                =                                                                                                                                                                                                                                                                                                                                                                                                                                    V                                              drive                                                                                        ·                                                                                          C                                              41                                                                                                                                -                                                                                                                                    V                                              drive                                                                                        ·                                                                                          C                                              42                                                                                                                                +                                                                                                                                    V                                              drive                                                                                        ·                                                                                                                                                                                                                                                                                                                                                                    C                                            43                                                                                    +                                                                                                                                    V                                              drive                                                                                        ·                                                                                          C                                              44                                                                                                                                                                                                                                                                                                                C                                    int                                                                                                                                                                                                                                                                                            X                                    ⁢                                                                                                                                                  ⁢                                                                          4                                      ·                                                                              (                                                                                                                              C                                            41                                                                                    +                                                                                      C                                            42                                                                                    +                                                                                      C                                            43                                                                                    +                                                                                      C                                            44                                                                                    +                                                                                      C                                            int                                                                                                                          )                                                                                                                                                                                  C                                    int                                                                                                                                                                                +                                                                                                                    .                                                                          [                      Expression            ⁢                                                  ⁢            4                    ]                    
Here, a difference between signals Y3 and Y4 of output terminals of the differential amplifier 112 is provided by
                                          Y            ⁢                                                  ⁢            3                    -                      Y            ⁢                                                  ⁢            4                          =                                                                                                                                                V                        drive                                            ·                                              (                                                                              C                            31                                                    -                                                      C                            41                                                                          )                                                              -                                                                  V                        drive                                            ·                                              (                                                                              C                            32                                                    -                                                      C                            42                                                                          )                                                              +                                                                                                                                                                  V                        drive                                            ·                                              (                                                                              C                            33                                                    -                                                      C                            43                                                                          )                                                              +                                                                  V                        drive                                            ·                                              (                                                                              C                            34                                                    -                                                      C                            44                                                                          )                                                                                                                                C              int                                +                                                                                                                                        X                        ⁢                                                                                                  ⁢                                                  3                          ·                                                      (                                                                                          C                                31                                                            +                                                              C                                32                                                            +                                                              C                                33                                                            +                                                              C                                34                                                            +                                                              C                                int                                                                                      )                                                                                              -                                                                                                                                  X                      ⁢                                                                                          ⁢                                              4                        ·                                                  (                                                                                    C                              41                                                        +                                                          C                              42                                                        +                                                          C                              43                                                        +                                                          C                              44                                                        +                                                          C                              int                                                                                )                                                                                                                                                C                int                                      .                                              [                  Expression          ⁢                                          ⁢          5                ]            
Here, it is set that “C31+C32+C33+C34+Cint” and “C41+C42+C43+C44+Cint” are provided by a capacitance Call which is almost equal thereto. That is, it is assumed thatCall≈C31+C32+C33+c34+Cint Call≈C41+C42+C43+C44+Cint.  [Expression 6]
When a gain of the differential amplifier 112 is sufficiently large, X3−X4 is regarded as being almost zero, so that an output signal Y341 of the differential amplifier 112, which is obtained in the driving by the 1st Vector indicated in FIG. 10, is provided by the difference between the signals Y3 and Y4 of the output terminals of the differential amplifier 112 and able to be represented as
                                                                        Y                ⁢                                                                  ⁢                                  34                  1                                            =                            ⁢                                                Y                  ⁢                                                                          ⁢                  3                                -                                  Y                  ⁢                                                                          ⁢                  4                                                                                                        =                            ⁢                                                                    V                    drive                                                        C                    int                                                  [                                                      (                                                                  C                        31                                            -                                              C                        41                                                              )                                    -                                      (                                                                  C                        32                                            -                                              C                        42                                                              )                                    +                                                                                                                                        ⁢                                                      (                                                                  C                        33                                            -                                              C                        43                                                              )                                    +                                      (                                                                  C                        34                                            -                                              C                        44                                                              )                                                  ]                            +                                                (                                                            X                      ⁢                                                                                          ⁢                      3                                        -                                          X                      ⁢                                                                                          ⁢                      4                                                        )                                ⁢                                                      C                    all                                                        C                    int                                                                                                                          =                            ⁢                                                                    V                    drive                                                        C                    int                                                  [                                                      (                                                                  C                        31                                            -                                              C                        41                                                              )                                    -                                      (                                                                  C                        32                                            -                                              C                        42                                                              )                                    +                                                                                                                                        ⁢                                                      (                                                                  C                        33                                            -                                              C                        43                                                              )                                    +                                      (                                                                  C                        34                                            -                                              C                        44                                                              )                                                  ]                            .                                                          [                  Expression          ⁢                                          ⁢          7                ]            
When code sequences used for i-th driving, which are provided to the drive lines DL1 to DL4, in the code sequences indicated in FIG. 10, that is, the Drive 1, the Drive 2, the Drive 3 and the Drive 4 in the i-th Vector indicated in FIG. 10 are Di1, Di2, Di3 and Di4, respectively, the output signal Y34i of the differential amplifier 112 is provided by
                                                                        Y                ⁢                                                                  ⁢                                  34                  i                                            =                            ⁢                                                Y                  ⁢                                                                          ⁢                                      3                    i                                                  -                                  Y                  ⁢                                                                          ⁢                                      4                    i                                                                                                                          =                            ⁢                                                                    V                    drive                                                        C                    int                                                  [                                                                            D                                              i                        ⁢                                                                                                  ⁢                        1                                                              ⁡                                          (                                                                        C                          31                                                -                                                  C                          41                                                                    )                                                        +                                                            D                                              i                        ⁢                                                                                                  ⁢                        2                                                              ⁡                                          (                                                                        C                          32                                                -                                                  C                          42                                                                    )                                                        +                                                                                                                                        ⁢                                                                            D                                              i                        ⁢                                                                                                  ⁢                        3                                                              ⁡                                          (                                                                        C                          33                                                -                                                  C                          43                                                                    )                                                        +                                                            D                                              i                        ⁢                                                                                                  ⁢                        4                                                              ⁢                                        (                                                                  C                        34                                            -                                              C                        44                                                              )                                                  ]                            .                                                          [                  Expression          ⁢                                          ⁢          8                ]            
Thirty one signals Y341 to Y3431 are obtained by driving with the 1st vector to a 31th vector indicated in FIG. 10. By executing computation of inner products of the thirty one signals Y341 to Y3431 and four code sequences with the sequence length of 31 applied to the respective drive lines DL1 to DL4, electrostatic capacitances connected to the respective drive lines are able to be estimated.
For example, when estimation of the electrostatic capacitances C31 to C41 is performed by using a code sequence “Di1” used for driving of the drive line DL1, it is represented by a following formula.
                                          ∑                          i              =              1                        31                    ⁢                                          ⁢                                    (                                                Y                  ⁢                                                                          ⁢                                      3                    i                                                  -                                  Y                  ⁢                                                                          ⁢                                      4                    i                                                              )                        ⁢                          D                              i                ⁢                                                                  ⁢                1                                                    =                              ∑                          i              =              1                        31                    ⁢                                          ⁢                      (                                                                                V                    drive                                                        C                    int                                                  ⁡                                  [                                                                                    D                                                  i                          ⁢                                                                                                          ⁢                          1                                                                    ⁡                                              (                                                                              C                            31                                                    -                                                      C                            41                                                                          )                                                              +                                                                  D                                                  i                          ⁢                                                                                                          ⁢                          2                                                                    ⁡                                              (                                                                              C                            32                                                    -                                                      C                            42                                                                          )                                                              +                                                                  D                                                  i                          ⁢                                                                                                          ⁢                          3                                                                    ⁡                                              (                                                                              C                            33                                                    -                                                      C                            43                                                                          )                                                              +                                                                  D                                                  i                          ⁢                                                                                                          ⁢                          4                                                                    ⁡                                              (                                                                              C                            34                                                    -                                                      C                            44                                                                          )                                                                              ]                                            ⁢                              D                                  i                  ⁢                                                                          ⁢                  1                                                      )                                              [                  Expression          ⁢                                          ⁢          9                ]            
Here, an M-sequence is known that an inner product of the same sequences takes the same value as a sequence length and an inner product of different sequences takes a value of −1. Accordingly, the aforementioned formula becomes
                                          ∑                          i              =              1                        31                    ⁢                                          ⁢                                    (                                                Y                  ⁢                                                                          ⁢                                      3                    i                                                  -                                  Y                  ⁢                                                                          ⁢                                      4                    i                                                              )                        ⁢                          D                              i                ⁢                                                                  ⁢                1                                                    =                                                            V                drive                                            C                int                                      ⁡                          [                                                31                  ⁢                                      (                                                                  C                        31                                            -                                              C                        41                                                              )                                                  -                                  (                                                            C                      32                                        -                                          C                      42                                                        )                                -                                  (                                                            C                      33                                        -                                          C                      43                                                        )                                -                                  (                                                            C                      34                                        -                                          C                      44                                                        )                                            ]                                .                                    [                  Expression          ⁢                                          ⁢          10                ]            
Here, if the electrostatic capacitance values C31 to C44 of the respective electrostatic capacitances C31 to C44 have the almost same value by assuming that all the sense lines SL1 to SL4 and all the drive lines DL1 to DL4 are respectively created with a uniform width, a coefficient by which the electrostatic capacitances C31 to C41 are multiplied is thirty-one times larger than those of other electrostatic capacitances C32 to C42, C33 to C43 and C34 to C44, so that influence of other electrostatic capacitances C32 to C42, C33 to C43 and C34 to C44 becomes negligibly small and the aforementioned formula is able to be simplified as
                                                        ∑                              i                =                1                            31                        ⁢                                                  ⁢                                          (                                                      Y                    ⁢                                                                                  ⁢                                          3                      i                                                        -                                      Y                    ⁢                                                                                  ⁢                                          4                      i                                                                      )                            ⁢                              D                                  i                  ⁢                                                                          ⁢                  1                                                              ≈                                                    V                drive                                            C                int                                      ⁡                          [                              31                ⁢                                  (                                                            C                      31                                        -                                          C                      41                                                        )                                            ]                                      ,                            [                  Expression          ⁢                                          ⁢          11                ]            
so that the electrostatic capacitance values C31 to C41 of the electrostatic capacitances C31 to C41 are able to be estimated.